1. FIELD OF THE INVENTION
The present invention relates to an IC card and, more particularly, to a structure of an IC card for housing an IC module in a card base.
2. DESCRIPTION OF THE PRIOR ART
A rapid improvement has recently been made in development of an IC card incorporating an IC chip including a CPU and memories. Since this IC card has a larger storage capacity than a conventional IC card, its use in place of a bankbook or a credit card is taken into consideration.
A conventional IC card and an IC module housed in the IC card will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing an outer appearance of a conventional IC card. FIG. 2 is a sectional view taken along a line A - A in FIG. 1. FIG. 3 is a perspective view showing an outer appearance of a card base constituting the IC card. FIG. 4 is a perspective view showing an outer appearance of an IC module. FIG. 5 is a sectional view showing a main part of another conventional IC card.
Referring to FIG. 1, a plurality of contact patterns 32c of an IC module 32 (to be described later) are formed on a surface of an IC card 30 so as to be exposed. In addition, various print patterns 30a are formed on the same surface. An overall card shape is defined by a plastic card base 31 shown in FIG. 3. A board recess 31a and a sealing recess 31b for housing the IC module 32 are formed in the card base 31. The card base 31 is made of, e.g., ABS resin by injection molding. As shown in FIG. 4, the IC module 32 is designed such that an IC chip 33 is bonded to a circuit board 32a made of a glass epoxy resin, and a seal portion 32b is formed on the IC chip 33 by using a sealing resin, while the contact patterns shown in FIG. 1 are formed on the lower surface of the circuit board 32a.
As shown in FIG. 2, the seal portion 32b of the IC module 32 is housed in the sealing recess 31b of the card base 31, and the circuit board 32a is housed in the board recess 31a while the outer periphery of the board 32a is restricted by the recess 31a. In this case, the IC module 32 is housed such that the surface of the contact patterns 32c is located on the same plane as that of the card base 31. An adhesive (not shown) is coated between the circuit board 32a, the sealing portion 32b, the board recess 31a, and the sealing recess 31b, and is heated and hardened, thus fixing the IC module 32 to the card base 31.
Generally, the IC card 30 has a thickness of about 0.8 mm, and must have elasticity enough to allow bending to a certain extent so as not to be destroyed by an external force generated when a user carries or uses it. Therefore, it is required that the card base 31 has elasticity while the seal portion 32b of the IC module 32 has rigidity, and that the IC module 32 is firmly fixed to the card base 31.
Since the material of the circuit board 32a and the seal portion 32b constituting the IC module 32 is different from that of the card base 31, it is difficult to obtain an adhesive capable of reliably bonding them to each other. In addition, since a bonding force greatly varies, in the case of the above-described IC card 30, when the card base 31 is flexed, peeling occurs at a bonding portion between the card base 31 and the IC module 32. As a result, the IC module 32 is removed from the base 31.
When an adhesive is heated to be hardened, the adhesive leaks from a gap between the IC module 32 and the circuit board 32a depending on an amount of the adhesive and a bonding position. As a result, the surface of card base 31 on which the print patterns 30a are formed may be contaminated.
In addition, the card base 31 tends to be deformed because of heat generated when an adhesive is heated and hardened.
Moreover, an adhesive has poor handling properties and workability. Therefore, a demand has arisen for an IC card structure allowing an IC module to be housed in a card base without using an adhesive. For this purpose, Japanese Patent Laid-Open (Kokai) No. 61-204788 discloses an IC card structure for fixing an IC module to a card base without using an adhesive.
This IC card structure will be described in detail below with reference to FIG. 5. A through hole 40a is formed in a card base 40 constituting an IC card. An IC module 41 is housed in the through hole 40a through a ring-like coupling member 44. In addition, reinforcing members 42 and 43 are arranged on the upper and lower surfaces of the IC module 41 and are fixed to the card base 40. Note that a hole 42a is formed in the reinforcing member 42 on the side of contact patterns 41a so as to expose the contact patterns 41a.
According to the above-described IC card structure, if the reinforcing members 42 and 43 and the coupling member 44 are made of a metal material, they can be firmly coupled to each other by soldering or high-frequency welding. Therefore, unlike the conventional IC card, the card base and the IC module need not be integrally bonded to each other through an adhesive.
In the above-described IC card, however, the following problems are posed.
In the conventional IC card, in order to reliably connect contact patterns to an R/W (read/writer) unit for reading/writing data, the contact patterns are formed such that their surfaces are located on the same plane as the surface of the card base. In the IC card described above, however, since the reinforcing member 42 is thicker than each contact pattern 41a, the contact pattern 41a is placed at a position lower than the surface of the card base 40. For this reason, connection between the contact patterns 41a and the R/W unit becomes unstable.
In addition, even if the outer size of the IC module 41, the inner and outer diameters of the coupling member 44, and the inner diameter of the through hole 40a are slightly deviated in size, fixing of the IC module becomes unstable. This may cause a positional error of the contact patterns 41a. Moreover, in this IC card structure, only the reinforcing members 42 and 43 and the coupling member 44 are bonded to each other, and hence the card base 40 and the IC module 41 are not firmly fixed to each other. Therefore, while a user carries the IC card, the positions of the base 40 and the module 41 may be offset. This may cause a positional error of the contact patterns 41a. Therefore, in order to solve this problem, an adhesive must be locally applied to the IC module 41 and the card base 40 in the same manner as in the IC card shown in FIG. 2.